Each November the earth passes through the field of debris left by the comet Temple-Tuttle. As the bits of dust and rock hit our planet's atmosphere at high speeds, they burn up and create flashes of light. Scientists expect that this year's meteor shower, which started last Thursday, will be particularly impressive because the earth will traverse two trails left by the comet. For North American sky watchers, the highlight of the show should occur late tonight and early Tuesday morning, between the hours of 11 p.m and 6:00 a.m. EST.

The Leonid meteor shower is named after the area in the sky where it originates. "Leonid meteors stream out of a point in [the constellation] Leo called the radiant," says Bill Cooke of the NASA Marshall Space Flight Center. "This year the radiant is easy to find because it's near the bright planet Jupiter." Astronomers predict that the height of the storm will bring a few meteors each minute. But this year's shower has one drawback compared to last year's impressive display: a full moon. Although the moon's light will outshine some of the fainter meteors, Don Yeomans of NASA's Jet Propulsion Laboratory remains confident that the storm will provide a good show. "Even with the full moon," he says, "this year's Leonids will probably be better than any other for the next hundred years." That's because predictions suggest that the earth won't intersect a really dense Tempel-Tuttle debris stream again until 2098 or 2131.

Researchers at NASA are mining the meteor storm for scientific data. "We are looking for clues about the diversity of comets and their impact on the chemistry of life's origins on Earth," says Peter Jenniskens of the SETI institute and NASA's Ames Research Center. An airborne laboratory carrying high-speed cameras, radio receivers and human observers is tracking the storm over Spain. The trip, explains NASA scientist John Hillman, "promises an important and unique database for the development of instruments targeted at in situ sampling of cometary materials and for the future definition of comet missions."